Electric current measurements within electric motor control are mainly based on measurement of a voltage drop across a shunt resistor. For high current applications, however, Hall sensors are used. In both cases, since the voltage to be measured is small and the environment of an electric motor control is typically noisy, the use of a Sigma-Delta modulator is advantageous because of its capability to convert low voltage inputs with high accuracy and low noise. A Sigma-Delta modulator converts an analog input signal into a digital data stream. The principles of Sigma-Delta modulation are described in “CMOS: Mixed-Signal Circuit Design, Chapter 32: Noise Shaping Data Converters” by Russel J. Baker, John Wiley & Sons.
The accuracy of current measurement with a Hall sensor and a Sigma-Delta modulator is affected by several factors. Since the Hall voltage is proportional to the current applied to the Hall sensor, a first factor is the temperature drift of the current supplied to the Hall sensor, such current being in turn dependent on the temperature behavior of a reference voltage source used in the current source that provides the current to the Hall sensor. Another factor is the temperature dependent gain drift of the Sigma-Delta modulator.